Hydrogels are highly hydrated macromolecular networks, dispersed in water or other biological fluids. Hydrogels are used in widespread biomedical applications including drug delivery vehicles, cell encapsulation matrices and tissue engineering scaffolds. Hydrogels are porous and nanostructured materials that exhibit properties such as microporosity, surface area, low density, transparency and low heat conductivity similar to natural tissue. S. Kistler first synthesized hydrogels in the 1930's, e.g. (Kistler, 1931). Kistler fabricated them from a variety of naturally-occurring materials such as cellulose-derivatives.
A hydrogel is a material that absorbs solvents (such as water), undergoes rapid swelling without discernible dissolution, and exhibits a three-dimensional microporous network where solvent is absorbed and capable of flowing through the network. Hydrogels may be uncross-linked or cross-linked. Uncross-linked hydrogels are typically able to absorb water but do not dissolve due to the presence of hydrophobic and hydrophilic regions interacting together. Covalently cross-linked networks of hydrophilic polymers, including water soluble polymers, are traditionally denoted as hydrogels in the hydrated state.
A common use of hydrogels is in soft contact lenses. They are also used as burn and wound dressings to facilitate healing, with and without incorporated drugs that can be released from the gel matrix (DiCosmo and DiTizio, 2001; Moro et al., 1981; St. John and Moro, 2011). Hydrogels are also used as coatings to enhance the wettability of the surfaces of medical devices such as blood filters (Hagiwara et al., 1996). Another example of their use is as devices for the sustained release of biologically active substances. For example, Moro et al. discloses a method of preparing a hydrophilic reservoir drug delivery device (Moro et al., 1994).
There are many applications that require the removal of specific molecules (agents) within an aqueous sample. One example is detecting the presence of molecules—such molecules can be detected by removing them from the sample and determining their presence. Furthermore, such collected molecules can be analyzed or even quantified. Alternatively, in some cases, removing certain molecules from a sample can decrease the interference those molecules may have when detecting or analyzing another molecule of interest. In an analytical diagnostic test, binding out targeted molecules can be a means to both concentrate and collect those molecules for detection or analysis; or, their removal can be a means to remove molecules that interfere with the detection or analysis of another analyte. For example, in a medical diagnostic test, target molecules for detection or analysis can include disease or pathogen markers from a biological sample. In an environmental diagnostic test, the target molecule can involve a pollutant, a toxin, a micro-organism, or associated markers of these from an aqueous sample. An example of a biothreat diagnostic test can involve binding a viral agent, a microbial agent, a biotoxin, or chemical marker from a sample. Medical apparatuses can be used to benefit a patient, including binding biologically active molecules that result from disease, or that have a detrimental effect on health and patient healing. An example of a research tool would include the binding of diluted biological or chemical molecules from a reaction, test solution or research organism.
Current methods for binding out agents and concentrating them rely heavily on mechanical action whereby a sample is introduced with binding molecules such as antibodies or aptamers, allowed time to mix in order to enable dispersion of the binding molecules and, following recognition and binding of target molecules, the use of centrifugation, gravity or magnetic fields to separate the complexed binding molecules from the starting material for detection or analysis.